1. Field of the Invention
The present invention relates to a rotary cutter for cutting consecutively such sheet material as paper strip, paper board, synthetic resin film, etc. into pieces with desired length, in particular, to a contact pressure control method for this kind of rotary cutter and a device therefor.
2. Description of the Prior Art
The sheet product such as paper, film, etc., includes a group of flat product and another group of roll product. The flat product is formed by cutting the product supplied from a sheet manufacturing line or the roll product in the feeding direction and the width direction of the product with a slitter and a fly knife in a cutter or a sheeter.
Regarding the cutting method, a slitter employing the type of thin upper and lower blades produces little paper dust even in cutting the paper of 600 g/m2. But there are some problems in cutting with a fly knife. In the type with one fixed blade shown in FIG. 12 of attached drawings, for example, a paper sheet 1 is cut by a fixed blade 2 and a rotating blade 3, but this type has not enough power for cutting a thick paper. To cut the thick paper, a twin rotor type with upper and lower rotating blades 4 and 5 shown in FIG. 13 has been developed and is in main use at present. In this twin rotor type, however, an adjusting operation for matching relative positions of the upper and the lower rotating blades is so difficult that even a skilled worker needs six to eight hours for the blade position matching in some cases.
To solve these problems, a rotary cutter with a structure shown in FIG. 14 has been developed. The details of the structure and the operation of this rotary cutter are disclosed in the Japanese Patent Laid-Open Publication Number 6-304895/1994. Briefly described, the rotary cutter comprises a knife rotor 6, a plain rotor 7, and a feed roller 8. The knife rotor 6 has knives 9a, 9b which are mounted on the two portions of outer surface of said knife rotor and arranged in the longitudinal direction of the knife rotor. In this rotary cutter, the paper sheet 1 which is sandwiched between and fed from the plain rotor 7 driven by a variable speed motor and the feed roller 8 is cut by the knife 9a attached to the outer surface of the knife rotor 6 driven by a servo motor while the paper 1 is pressed against the plain rotor 7. The knife rotor 6 is controlled and driven so as to rotate at the same speed with that of the fed paper 1 only when the attached knives 9a, 9b contact the paper 1 to be cut.
The structure and operation of this rotary cutter have been described above and a holding mechanism of the respective knives 9a, 9b in the knife rotor 6 is, for example, as shown in an enlarged partial sectional view of FIG. 15. As shown in FIG. 15, the knife 9a is attached to the knife rotor 6 as follows. At first, a knife holder 12 equipped with a permanent magnet 11 is fixed by a bolt 13 into a groove 10 formed in the longitudinal direction of the knife rotor 6, and then, into an insertion groove 14 formed consequently, the knife 9a is simply inserted, and, as a result, the knife can be fixed to the knife rotor 6 due to the magnetic effect. Accordingly, the knife replacement service can be carried out within a few seconds and the period for knife replacement has surprisingly been reduced.
But in such material as film where a cut section is expected to be a similar one cut by a guillotine, even a rotary cutter as described above needs the blade position matching, that is, the clearance between the plain rotor 7 and the position of knife rotor 6 in FIG. 14 and FIG. 15 must be adjusted. Traditionally, the clearance is adjusted in a manner that the relative position of the upper and lower blades is adjusted by carefully examining the cut section of a sheet or carefully listening to the sound at the cutting, and therefore, the adjusting operation is still a difficult work.
Furthermore, the contact pressure, even if once adjusted, changes in the long hour running due to the knife wear itself or to the variation in size resulting from the expansion and contraction of the knife and surrounding machine components. It is very difficult to compensate these factors.
The object of the present invention is to provide a contact pressure control method and a device for a rotary cutter which solves the problems of the conventional technology as described above.